i think part of why we are not bothered by stories where the main character loses their memories or is permanently regressed or broken into a blissed out pet who hardly knows who they are anymore, and in fact find them extremely comfy and seek them out, is because we experienced a taste of that on mushrooms one time.
sitting on the floor after a profound experience losing our sense of self, no idea who the friendly strangers (our closest partners/friends) watching over us were but knowing they were safe and we were going to be okay, no idea who we were, no idea of our name or how we got there, no real understanding of the world, no memories (and all this accompanied by intense sensory pleasure and perceptual alteration)
and the thing is, that this has kind of convinced us that there is a sort of spirit for every given self within a body, which exists outside of memories. a self-semblance or recurrence, if you will. because even though we couldn't remember who we were, we still joked in ways that were recognizable to our friends as Us, in ways that, looking back on the memories now, were recognizable to us as Us
it's a little strange to articulate but the identity of a spirit and the self-semblance of a spirit are two separate things. a spirit can lose their identity and the self-semblance can remain. your memories don't make us who we are so much as tell us who we are; it's the events those memories describe which shaped us (even if the events are actually fictitious). the memories are the ripples but even if the ripples fade the stone is still in the pond.
i think we just aren't particularly afraid of losing our memories after this experience. memory loss is probably in many cases more upsetting for the friends of the amnesiac than for the amnesiac themselves.